Transmissions featuring floating transmission mainshaft gears such as associated with twin countershaft transmissions are well know and examples of which can be found in U.S. Pat. Nos. 3,237,472; 3,238,613; 3,425,290; and 3,885,446, the disclosures of which are incorporated herein by reference.
Such transmissions generally feature a plurality of floating mainshaft gears that encircle the mainshaft and are supported and driven by countershaft gears, typically two countershaft gears, that are mounted on a pair of countershafts disposed on opposite sides of the mainshaft.
The mainshaft gears are characteristically clutched to the mainshaft by means of a clutch mechanism that slides along external splines extending axially along the mainshaft and has radially inwardly extending teeth or splines that engage internal teeth or splines on the mainshaft gear so as to cause rotation of the mainshaft when the mainshaft gear is clutched thereto.
A problem long ago recognized has been the potential transfer of axial thrust to a mainshaft gear being clutched due to their characteristic close proximity to each other. In view of such, a variety of solutions have been devised over past years for the transmitting axial thrust imparted by an axially moving clutch to the mainshaft rather than to the gear adjacent the gear being clutched to the mainshaft.
Such solutions have generally been in the form of gear retainer(s) of one type or another that characteristically limit axial movement of the mainshaft gears to prevent them from engaging each other whether or not one of them is being clutched to the mainshaft.
One example of a retainer assembly for limiting axial movement of a transmission gear is disclosed in U.S. Pat. No. 2,397,905, the disclosure of which is incorporated herein by reference. Here however, a costly and expensive pivotal woodruff key is required to lock a thrust collar onto external splines of the mainshaft to prevent a gear from moving axially.
An example of a splined thrust washer for transmitting axial thrust from a gear set to a propeller drive shaft is disclosed in U.S. Pat. No. 3,894,621, the disclosure of which is incorporated herein by reference. Here, a splined thrust washer (52) is slid axially along the shaft splines to a transverse groove adjacent a stepped shoulder on the shaft and is held in place against the shoulder by a splined collar (30). Thrust washer (52) is operative to transmit axial thrust of only one gear to the propeller shaft and in addition to requiring the use of Collar (30), also requires costly and complex machining of a stepped configuration to the Propeller shaft exterior.
A more recent example of a transmission mainshaft gear retainer for preventing axial movement of two closely spaced gears to prevent transfer of axial thrust force therebetween is disclosed in U.S. Pat. No. 4,034,620, the disclosure of which is incorporated herein by reference. Here a thrust ring (104) is splined to the mainshaft between two adjacent gears and is held in place by means of snap rings (108, 110) on opposite sides thereof. The gears are further required to have costly and complex mating tongue and groove configurations that operate in conjunction with an additional snap ring (102) to limit movement of the gears away from each other.
In view of the above, a need exists to provide a simple and low cost means for transmitting axial thrust imparted by a clutch to a floating mainshaft gear being clutched to the mainshaft rather than to an adjoining gear by retaining means that can be easily assembled into the mainshaft and rotate in unison with the mainshaft gear being clutched.